U.S. patent application number 10/620036 was filed with the patent office on 2004-01-22 for die attach process using cornercube offset tool.
Invention is credited to Beatson, David T., Ditri, John, Eder, James E., Hoffman, Christian.
Application Number | 20040012784 10/620036 |
Document ID | / |
Family ID | 27732452 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040012784 |
Kind Code |
A1 |
Beatson, David T. ; et
al. |
January 22, 2004 |
Die attach process using cornercube offset tool
Abstract
A system and method having applications in semiconductor areas
for accurate die placement on a substrate that takes into account
any positional offset from the reference position due to variations
caused by thermal change and other nonrandom systemic effects. The
system includes an offset alignment tool having a plurality of
internal reflection surfaces and located below a vision plane of
the substrate, and an optical detector to receive an indirect image
of a bottom surface of the die through the alignment tool, such
that the die is accurately positioned on the substrate based on the
indirect image received by the optical detector. The method
comprises the steps of providing a cornercube offset alignment tool
having a plurality of total internal reflection surfaces below a
vision plane of the die, and receiving an indirect image of the die
tool through the cornercube offset tool.
Inventors: |
Beatson, David T.; (Kennett
Square, PA) ; Hoffman, Christian; (Willow Grove,
PA) ; Eder, James E.; (Doylestown, PA) ;
Ditri, John; (Huntingdon Valley, PA) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
27732452 |
Appl. No.: |
10/620036 |
Filed: |
July 15, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10620036 |
Jul 15, 2003 |
|
|
|
10075899 |
Feb 14, 2002 |
|
|
|
10075899 |
Feb 14, 2002 |
|
|
|
09912024 |
Jul 24, 2001 |
|
|
|
6412683 |
|
|
|
|
Current U.S.
Class: |
356/400 |
Current CPC
Class: |
B23K 20/002 20130101;
B23K 31/12 20130101; B23K 2101/40 20180801; H01L 21/681 20130101;
H01L 2224/78301 20130101; B23K 20/10 20130101 |
Class at
Publication: |
356/400 |
International
Class: |
G01B 011/00 |
Claims
What is claimed:
1. A system for positioning a die on a substrate, the system
comprising: an alignment tool having a plurality of internal
reflection surfaces, the alignment tool located below a vision
plane of the substrate; and an optical detector to receive an
indirect image of a bottom surface of the die through the alignment
tool, wherein the die is positioned on the substrate based on the
indirect image received by the optical detector for correct
alignment of the die on the substrate.
2. The system according to claim 1, wherein optical detector is
positioned above a top surface of the offset alignment tool.
3. The system according to claim 1, wherein the alignment tool
comprises a plurality of cornercube offset tools, each one having a
respective plurality of internal reflection surfaces.
4. The system according to claim 1, wherein the alignment tool is
formed from one of fused silica, sapphire, diamond, calcium
fluoride and an optical glass.
5. The system according to claim 1, wherein a vertex of the
cornercube offset tool is located at a position about midway
between an optical axis of the optical detector and an optical axis
of the die.
6. The system according to claim 1, further comprising a die
placement tool, wherein the alignment of the die on the substrate
is based on a positional offset of the die placement tool from a
reference position.
7. A system for positioning a die on a substrate, the system
comprising: a plurality of cornercube offset tools each having a
respective plurality of internal reflection surfaces, the plurality
of cornercube offset tools located below a vision plane of the
substrate; and an optical detector to receive an indirect image of
a bottom surface of the die through at least one of the plurality
of cornercube offset tools, wherein the die is positioned on the
substrate based on the indirect image received by the optical
detector.
8. The system according to claim 7, wherein a camera receives the
indirect image of the bottom surface of the die through the
cornercube offset tool.
9. The system according to claim 7, wherein a vertex of the
cornercube offset tool is located at a position about midway
between an optical axis of the optical detector and an optical axis
of the die.
10. The system according to claim 9, wherein a focal plane of the
system is positioned above the vertex of the cornercube offset
tool.
11. The system according to claim 7, further comprising: a
respective plurality of first lenses disposed between the optical
input means and each of the plurality of cornercube offset tools;
and a respective plurality second lenses disposed between the die
and each of the plurality of cornercube offset tools.
12. The system according to claim 11, wherein the plurality of
first lenses and the plurality of second lenses are located below
the image plane.
13. The system according to claim 11, wherein the plurality of
first lenses and the plurality of second lenses each have a unitary
magnification factor.
14. The system according to claim 7, wherein each of the plurality
of cornercube offset tools are formed from one of fused silica,
sapphire, diamond, calcium fluoride and an optical glass.
15. The system according to claim 7, wherein each of the plurality
of the cornercube offset tools has an apex angle of about
90.degree., a second angle of about 45.degree. and a third angle of
about 45.degree..
16. The system according to claim 7, wherein optical detector is a
camera.
17. The system according to claim 16, wherein the camera is a CCD
camera.
18. The system according to claim 7, wherein the optical detector
is a CMOS imager.
19. The system according to claim 7, wherein the cornercube offset
tool has an index of refraction between about 1.5 and 1.7.
20. The system according to claim 7, wherein the cornercube offset
tool has an index of refraction of about 1.517.
21. The system according to claim 7, wherein the system is used
with light having a wavelength in the visible spectrum.
22. The system according to claim 7, wherein the system is used
with light having a wavelength between about 1-3000 nm.
23. The system according to claim 7, wherein the system is used
with light having a wavelength between about 630-690 nm.
24. The system according to claim 7, wherein the system is used
with light having a wavelength between about 1-400 nm.
25. The system according to claim 7, wherein the system is used
with light having a wavelength between about 700-3000 nm.
26. The system according to claim 7, wherein the system is used
with light having a wavelength of about 660 nm.
27. The system according to claim 7, further comprising: a lens
positioned in both i) a first optical axis between the optical
input means and respective ones of the plurality of cornercube
offset tools and ii) a second optical axis between the die and the
cornercube offset tool, wherein the first and second optical axis
are substantially parallel to one another.
28. A vision system for use with an optical detector for
positioning a die on a substrate, the system comprising: a
plurality of cornercube offset tools each having a plurality of
internal reflection surfaces, the plurality of cornercube offset
tools located below a vision plane of the die; a lens positioned in
both i) a first optical axis between the vision plane and each of
the plurality of cornercube offset tools and ii) a second optical
axis between the optical detector and the plurality of cornercube
offset tools, wherein the optical detector receives an indirect
image of a bottom surface of the die through at least one of the
plurality of cornercube offset tools.
29. The cornercube offset tool according to claim 28, wherein the
plurality of internal reflection surfaces are three internal
reflection surfaces.
30. A vision system according to claim 28, wherein the optical
detector is positioned above the image plane.
31. A vision system according to claim 28, wherein the first
optical axis and the second optical axis are substantially parallel
to one another.
32. The device according to claim 28, wherein the lens has a
unitary magnification factor.
33. The device according to claim 28, wherein the lens is a
respective plurality of first lenses positioned in the first
optical axis and a respective plurality of second lenses positioned
in the second optical axis.
34. The device according to claim 33, wherein the plurality of
first lenses and the plurality of second lenses each have a unitary
magnification factor.
35. A vision system for use with a bonding machine for placing a
die on a substrate, the system comprising: a cornercube offset tool
having three internal reflection surfaces, the cornercube offset
tool located below a vision plane of the bonding machine; and an
optical detector to receive an indirect image of the die through
the cornercube offset tool, wherein the die is placed on the
substrate based on the indirect image received by the optical
detector, for correct alignment of the die on the substrate.
36. A vision system according to claim 35, wherein at least one of
the internal reflection surfaces is a total internal reflection
surface.
37. A vision system according to claim 35, wherein the plurality of
internal reflection surfaces are total internal reflection
surfaces.
38. A vision system according to claim 35, further comprising a die
placement tool, wherein the alignment of the die on the substrate
is based on a positional offset of the die placement tool from a
reference position.
39. A system for positioning a die on a substrate, the system
comprising: image redirecting means disposed below a vision plane
of the substrate, the image redirecting means having a plurality of
internal reflection surfaces; and detecting means to receive an
indirect image of a bottom surface of the die through the image
redirecting means, wherein the die is positioned on the substrate
based on the indirect image received by the detecting system, for
correct alignment of die on the substrate.
40. A vision system according to claim 39, further comprising a die
placement means, wherein the alignment of the die on the substrate
is based on a positional offset of the die placement means from a
reference position.
41. A method for positioning a die on a substrate, the method
comprising the steps of: providing a cornercube offset tool below a
vision plane of the substrate, the cornercube offset tool having
three internal reflection surfaces; viewing an indirect image of
the die through the cornercube offset tool; identifying a feature
located on a bottom surface of the die based on the indirect image;
and placing the die on the substrate based on the identified
feature.
42. A method for positioning a die on a substrate, the method
comprising the steps of: positioning a plurality of cornercube
offset tools below a vision plane of the substrate; positioning a
first lens between each of the plurality of cornercube offset tools
and the die; positioning a second lens between each of the
plurality of cornercube offset tools and an optical input device;
and viewing a surface of the die through the first lens, the
cornercube offset tool, and the second lens.
43. A method for use with a bonding machine to place a die on a
substrate, the method comprising the steps of: positioning a
cornercube offset tool below a vision plane of the bonding machine;
positioning a lens between i) the vision plane and the cornercube
offset tool and ii) between an optical input device and the
cornercube offset tool; viewing a portion of a bottom surface of
the die through the cornercube offset tool and the lens; and
placing the die on the substrate based on the viewed portion of the
die.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/912,024 filed on Jul. 24, 2001.
FIELD OF THE INVENTION
[0002] This invention relates generally to the use of machine
vision systems for semiconductor chip bonding/attaching devices.
More specifically, the present invention relates to the use of a
corner cube retro-reflector as an offset alignment tool that
acquires indirect images of the bonding target during the die
attach process when the same lie outside the view of the imaging
system. From such images, coordinate information on position can be
obtained and any positional offset from a reference position of the
die bonding tool or die placement tool due to deviations caused by
thermal change or other nonrandom systemic errors can be taken into
account for correct alignment of wire bonding, die placement or
fiber placement tools.
BACKGROUND OF THE INVENTION
[0003] Semiconductor devices, such as integrated circuit chips, are
electrically connected to the leads on a lead frame by a process
known as wire bonding. The wire bonding operation involves placing
and connecting a wire to electrically connect a pad (first bond)
residing on the semiconductor die to a lead (second bond) in a lead
frame. Both the first and the second bonds have to be placed
accurately as dictated by requirements of the package. Once all the
appropriate pads on the chip have been wire bonded to the
appropriate leads on the lead frame, it can be packaged, often in
ceramic or plastic, to form an integrated circuit device. In a
typical application, a die or chip may have hundreds or thousands
of pads and leads that need to be connected.
[0004] There are many types of wire bonding equipment. Some use
thermal bonding, some use ultra-sonic bonding and some use a
combination of both. Prior to bonding, vision systems or image
processing systems (systems that capture images, digitize them and
use a computer to perform image analysis) are used on wire bonding
machines to align devices and guide the machine for correct bonding
placement.
[0005] In conventional systems, post attach inspection is used to
determine if relative changes in bonding or die placement tool
position are necessary to effect proper and accurate placement of
die or wire bonds. As such, these conventional systems can only
compensate for improper wire bonds or improper die placement after
such improper wire bonds or improper die placement actions occur,
thereby negatively effecting device yield and machine throughput.
These conventional systems have additional drawbacks in that they
are unable to easily compensate for variations in the system due to
thermal changes, for example. These changes require periodic
inspection of completed devices further impacting device yield and
negatively impacting manufacturing time.
[0006] In conventional systems the vision system (shown in FIG. 11)
consists of two image devices, a first image device 1104 placed
below the optical plane 1112 and upwardly viewing objects and a
second image device 1102 placed above the optical plane and
downwardly viewing objects. These conventional systems have
drawbacks in that in addition to requiring more than one image
device, they are unable to easily compensate for variations in the
system due to thermal changes, for example.
SUMMARY OF THE INVENTION
[0007] In view of the shortcomings of the prior art, it is an
object of the present invention to provide a method for attaching
an integrated circuit die to an underlying substrate using vision
system that takes into account variations due to temperature
changes and other nonrandom systemic effects.
[0008] The present invention is a vision system for use with a
semiconductor fabrication machine for accurate die alignment and
die placement. The system comprises an alignment tool having a
plurality of internal reflection surfaces, the alignment tool
located below a vision plane of the substrate; and an optical
detector to receive an indirect image of a bottom surface of the
die through the alignment tool.
[0009] According to another aspect of the invention, the vertex of
the alignment tool is located at a position about midway between an
optical axis of the optical detector and an optical axis of the
die.
[0010] According to a further aspect of the invention, the
alignment tool comprises a plurality of cornercube offset
tools.
[0011] According to still another aspect of the invention, the
focal plane of the vision system is positioned at or above the
alignment tool.
[0012] According to yet another aspect of the present invention,
the system includes a lens positioned between the alignment tool,
and i) the optical detector and ii) the die.
[0013] According to still another aspect of the present invention,
the system includes a first lens positioned between the optical
detector and the alignment tool and a second lens positioned
between the die and the alignment tool.
[0014] According to a further aspect of the present invention, the
first lens and the second lens are located at or below the image
plane.
[0015] According to another aspect of the present invention, the
first lens and the second lens are located in line with the image
plane.
[0016] According to yet a further aspect of the present invention,
the reflecting surfaces are three mutually perpendicular faces.
[0017] According to yet another aspect of the present invention,
the angle between each of the internal reflective surfaces and the
top surface of the corner cube offset tool is about 45.degree..
[0018] According to still another aspect of the invention, the
optical detector is a CCD camera.
[0019] According to yet another aspect of the invention, the
optical detector is a CMOS imager.
[0020] According to yet a further aspect of the invention, the
optical detector is a position sensitive detector.
[0021] According to an exemplary method of the present invention, a
cornercube offset tool is positioned below a vision plane of the
die; a lens is positioned between i) the die and the cornercube
offset tool and ii) between an optical imager and the cornercube
offset tool; and the die is viewed indirectly through the
cornercube offset tool and the lens.
[0022] These and other aspects of the invention are set forth below
with reference to the drawings and the description of exemplary
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention is best understood from the following detailed
description when read in connection with the accompanying drawing.
It is emphasized that, according to common practice, the various
features of the drawing are not to scale. On the contrary, the
dimensions of the various features are arbitrarily expanded or
reduced for clarity. Included in the drawing are the following
Figures:
[0024] FIG. 1 is a perspective view of an exemplary embodiment of
the present invention;
[0025] FIG. 2A is a side view of image ray traces according to a
first exemplary embodiment of the present invention;
[0026] FIG. 2B is a side view of image ray traces according to a
second exemplary embodiment of the present invention;
[0027] FIG. 3 is a perspective view of image ray traces according
to an exemplary embodiment of the present invention;
[0028] FIGS. 4A and 4B are perspective and side views,
respectively, of an exemplary embodiment of the present
invention;
[0029] FIG. 5 illustrates the telecentricity of an exemplary
embodiment of the present invention;
[0030] FIG. 6 is a detailed view of an exemplary retroreflective
cornercube offset tool according to the present invention;
[0031] FIGS. 7A-7C illustrate the effect of tilt about the vertex
of the cornercube tool of the exemplary vision system;
[0032] FIGS. 8A-8C illustrate the effect of tilt about the X and Y
axis of the exemplary vision system;
[0033] FIG. 9 is a side view of image ray traces according to a
third exemplary embodiment of the present invention;
[0034] FIG. 10A is a perspective view of a fourth exemplary
embodiment of the present invention;
[0035] FIG. 10B is a plan view of the exemplary embodiment of FIG.
10A;
[0036] FIGS. 10C-10D are views of a lens element according to an
exemplary embodiment of the present invention; and
[0037] FIG. 11 is a vision system according to the prior art.
DETAILED DESCRIPTION
[0038] The entire disclosure of U.S. patent application Ser. No.
09/912,024 filed on Jul. 24, 2001 is expressly incorporated by
reference herein
[0039] Referring to FIG. 1 a perspective view of an exemplary
embodiment of the present invention is shown. The system is
included in wire bonding machine 100, and employs a cornercube 106,
having a plurality of internal reflection surfaces (best shown in
FIG. 6), located at or below image plane 112 of bonding tool
104.
[0040] In an exemplary embodiment, cornercube offset alignment tool
109 (comprising cornercube 106 and lens elements 108, 110), has a
total of three internal reflection surfaces, 218, 220, and 221
(best shown in FIG. 6 and described below). In another exemplary
embodiment, cornercube 106 may have a plurality of total internal
reflective surfaces. In one exemplary embodiment, cornercube 106 is
formed from fused silica, sapphire, diamond, calcium fluoride or
other optical glass. Note, optical quality glass, such as BK7 made
by Schott Glass Technologies of Duryea, Pa., may also be used. Note
also, that materials for cornercube 106 can be selected for maximum
transmission with respect to the desired operating wavelength.
[0041] Optical imaging unit 102, such as a CCD imager, CMOS imager,
or a camera, for example, is mounted above image plane 112 in order
to receive an indirect image of bonding tool 104 through cornercube
offset alignment tool 109. In another exemplary embodiment, a
position sensitive detector (PSD), such as that manufactured by
Ionwerks Inc., of Houston, Tex., may also be used as optical
imaging unit 102. In such an embodiment, when the hole in bonding
tool 104 is illuminated, such as by using an optical fiber for
example, the PSD can be utilized to record the position of the spot
of light exiting bonding tool 104. It is also contemplated that the
PSD may be quad cell or bi-cell detector, as desired.
[0042] In the exemplary embodiment, the focal point of the vision
system (coincident with imaginary plane 211 shown in FIG. 2A) is
located above bottom surface 223 (shown in FIG. 2A) of cornercube
106. In addition, the exemplary embodiment includes two preferably
identical lens elements 108, 110 located at or below image plane
112. Another embodiment, shown in FIG. 2B, includes a single lens
element 205 located below image plane 112 and in line with optical
axes 114, 116. Hereinafter, the combination of cornercube 106, and
lens elements 108, 110 (or lens element 205) will be referred to as
assembly 109.
[0043] Image plane 112 of cornercube 106, including lens elements
108, 110, is positioned at the object plane of optical imaging unit
102. In other words, the object plane of cornercube 106 and lens
elements 108, 110 are aligned to bonding tool 104 which also lies
in image plane 112. In the exemplary embodiment, lens elements 108,
110 (or 205) preferably have a unitary magnification factor. First
lens element 108 is positioned in a first optical axis 114 between
bonding tool 104 and cornercube 106. Second lens element 110 is
substantially in the same plane as that of first lens element 108
and is positioned in a second optical axis 116 between optical
imaging unit 102 and cornercube 106. In one exemplary embodiment,
first and second optical axes 114 and 116 are substantially
parallel to one another, and are spaced apart from on another based
on specific design considerations of bonding machine 100. In one
exemplary embodiment the distance 118 between first optical axis
114 and second optical axis 116 is about 0.400 in. (10.160 mm.)
although distance 118 may be as small as about 0.100 in. (2.54 mm)
depending on design considerations related to the bonding
machine.
[0044] FIG. 2A is a detailed side view of image ray traces and
illustrates the general imaging concept of an exemplary embodiment
of the present invention. In FIG. 2A, exemplary ray traces 210, 214
are separated for clarity to illustrate the relative immunity of
the resultant image due to positional changes. The same distance
also separates the image points because lens elements 108, 110
serve as unitary magnification relays. FIG. 2A also demonstrates
how changes in the bonding tool 104 position are compensated for.
For example, once conventional methods have been used to accurately
measure the distance between imaging unit 102 and bonding tool 104
(shown in FIG. 1), the present invention is able to compensate for
changes in the bonding tool 104 (or pick/place tool 114 discussed
below with reference to FIG. 10A) offset position 222 due to
changes in the system. The location of bonding tool 104 can be
accurately measured because cornercube 106 images bonding tool 104
onto image plane 112 of the optical system.
[0045] The reference position of bonding tool 104 is shown as a
reflected ray which travels from first position 202 along first
optical axis 114 (shown in FIG. 1), as direct image ray bundle 210
from first position 202 through first lens element 108. Direct
image ray bundle 210 continues along first optical axis 114 where
it then passes through top surface 226 of cornercube 106 onto first
internal reflection surface 218. Direct image ray bundle 210 is
then reflected onto second internal reflection surface 220, which
in turn directs it onto third internal reflective surface 221 (best
shown in FIG. 3). Next, direct image ray bundle 210 travels back
through top surface 226 of cornercube 106 as reflected image ray
bundle 212 along the second optical axis 116 (shown in FIG. 1) and
through second lens element 110 to image plane 112. It is reflected
image ray bundle 212 that is detected by imaging unit 102 as image
204.
[0046] Consider now that the position of bonding tool 104 is
displaced by a distance 222 due to a variation in system
temperature, for example. As shown in FIG. 2A, the displaced image
of bonding tool 104 is shown as position 206 and imaged along the
path of second position ray trace 214. As shown in FIG. 2A, direct
image ray bundle 214 travels along a path similar to that of direct
image ray bundle 210 from first position 202. Second position 206
image travels as a direct image ray bundle 214, through first lens
element 108. Direct image ray bundle 214 then passes through top
surface 226 of cornercube 106 onto first internal reflection
surface 218. Direct image ray bundle 214 is then reflected onto
second internal reflection surface 220, which in turn directs it
onto third internal reflection surface 221 (best shown in FIG. 3).
Next, direct image ray bundle 214 travels through top surface 226
of cornercube 106 as reflected image ray bundle 216 and through
second lens element 110 to image plane 112. Reflected image ray
bundle 216 is viewed as a reflected image by imaging unit 102 as
being in second position 208. Although the above example was
described based on positional changes along the X axis, it is
equally applicable to changes along the Y axis.
[0047] As illustrated, the original displacement of bonding tool
104, shown as offset position 222, is evidenced by the difference
224 in the measured location of bonding tool 104 at second position
208 with respect to reference location 204. As evidenced by the
above illustration, a positional shift in assembly 109 does not
affect the reflected image as viewed by imaging unit 102. In other
words, assembly 109 of the present invention may be translated
along one or both the X and Y axes such that the image of the
bonding tool 104 appears relatively stationary to imaging unit 102.
There will be some minimal degree of error, however, in the
measured position of bonding tool 104 due to distortion in the lens
system (discussed in detail below).
[0048] Referring again to FIG. 2A, vertex 228 (shown in phantom) of
cornercube offset alignment tool 109 is located at a position
approximately midway between first optical axis 114 and second
optical axis 116. To facilitate mounting of cornercube 106, a lower
portion 235 of the cornercube may be removed providing bottom
surface 223, which may be substantially parallel to top surface
226. Removal of lower portion 235 does not affect the reflection of
image rays since the image rays emanating from image plane 112 do
not impinge upon bottom surface 223.
[0049] Exemplary cornercube 106 comprises top surface 226, first
reflective surface 218, bottom surface 223, second reflective
surface 220, and third reflective surface 221. If top surface 226
is set such that optical axes 114, 116 are normal to top surface
226, first reflective surface 218 will have a first angle 230 of
about 45.degree. relative to top surface 226, and a second angle
234 of about 135.degree. relative to bottom surface 223. Likewise,
ridgeline 225 (formed by the intersection of second and third
reflective surfaces 220 and 221) has similar angles 232 and 236
relative to top surface 226 and bottom surface 223, respectively.
In addition, second and third reflective surfaces 220 and 221 are
orthogonal to one another along ridgeline 225. In the exemplary
embodiment, bottom surface 223 of cornercube 106 may be used as a
mounting surface if desired. It should be noted, however, that it
is not necessary to form top surface 226 so that the image and
reflected rays are normal thereto. As such, the corner cube will
redirect the incident light or transmit image of bonding tool 104
parallel to itself with an offset equal to distance 118.
[0050] The present invention can be used with light in the visible,
UV and IR spectrums, and preferably with light having a wavelength
that exhibits total internal reflection based on the material from
which cornercube 106 is fabricated. The material selected to
fabricate cornercube offset alignment tool 109 is based on the
desired wavelength of light which the tool will pass. It is
contemplated that cornercube offset alignment tool 109 may be
fabricated to handle a predetermined range of light wavelengths
between the UV (1 nm) to the near IR (3000 nm). In a preferred
embodiment, the range of wavelength of light may be selected from
between about i) 1 and 400 nm, ii) 630 and 690 nm, and iii) 750 and
3000 nm. Illumination may also be provided by ambient light or by
the use of an artificial light source (not shown). In one exemplary
embodiment, typical optical glass, having an index of refraction of
1.5 to 1.7, may be used to fabricate cornercube 106. Note, the
index of refraction is based upon the material chosen for maximum
transmission at the desired operating wavelength. In one
embodiment, cornercube offset alignment tool 109 has an index of
refraction of about 1.517.
[0051] FIG. 3 is a perspective view of image ray traces according
to an exemplary embodiment of the present invention translated in a
direction perpendicular to the separation of lens elements 108,
110. The same image properties shown in FIG. 2A are also evident in
FIG. 3. For example, the reference position of bonding tool 104 is
represented by first position 302 and its image 304 is viewed as a
first direct image ray 310 which travels along first optical axis
114 through first lens element 108; passes through top surface 226
of cornercube 106; strikes first reflective surface 218 of
cornercube 106; travels through cornercube 106 in a path parallel
to top surface 226; strikes second reflective surface 220; strikes
third reflective surface 221 before exiting the cornercube 106
through top surface 226 and travels along second optical axis 116
through second lens element 110 onto image plane 112 and viewed by
imaging unit 102 at position 304. Positional displacement of
bonding tool 104 is also shown in FIG. 3 and is illustrated by the
path of the ray traces 314, 316 from second position 306 to second
viewed position 308.
[0052] FIGS. 4A-4B are perspective and side views, respectively, of
an exemplary embodiment of the present invention illustrating lens
elements 108, 110 and cornercube 106. The two lens elements 108,
110 (or 205) are preferably doublets located above the cornercube
106 based on their focal distance from image plane 112 and
imaginary plane 211. Doublets are preferred based on their superior
optical qualities. As illustrated in FIGS. 4A-4B, an exemplary
embodiment of cornercube 106 has three internal reflective
surfaces, 218, 220 and 221. As shown in FIG. 4B, the exterior edges
of lens elements 108, 110 and cornercube 106 are coincident with
one another.
[0053] FIG. 5 illustrates the telecentricity of an exemplary
embodiment of the image system of the present invention. As shown
in FIG. 5, lens elements 108, 110 produce a unitary magnification
and are arranged relative to cornercube 106 such that the
telecentricity of the machine vision system is maintained. Note
that front focal length 502 from lens element 108 to vertex 228 of
cornercube 106 is equal to front focal 502 from lens element 110 to
vertex 228 of cornercube 106. Note also, that back focal length 504
from lens element 108 to image plane 112 is equal to back focal
length 504 from lens element 110 to image plane 112.
[0054] FIG. 6 is a detailed view of an exemplary cornercube 106 of
the present invention. Note that internal reflection surface, 218
and ridgeline 225 allow an image of bonding tool 104 to be
translated in the X and Y directions. Note also, that the surfaces
of cornercube 106 are preferably ground so that a reflected beam is
parallel to the incident beam to within 5 arc seconds.
[0055] As shown in FIG. 6, surfaces 220 and 221 are orthogonal to
one another along ridgeline 225. In addition, the angle between
ridgeline 225 and surface 218 is about 90.degree.. Furthermore,
surface 218 and ridgeline form an angle of 45.degree. relative to
top surface 226 and bottom surface 223. Note also, that surfaces,
218, 220, and 221 meet to form triangular shaped bottom surface
223, which may be used to facilitate mounting of cornercube
106.
[0056] FIGS. 7A-7C illustrate the effect of tilt about the
orthogonal of cornercube offset alignment tool 109 in an exemplary
vision system. FIG. 7A is an overhead view of lens elements 108,
110 and cornercube 106. Exemplary image origins, 702, 704, 706, and
708 correspond to the position of image ray traces 210, 214 (shown
in FIG. 2A). Note that optic axis position 710 corresponds to the
position where the image of bonding tool 104 (shown in FIG. 1)
would be if cornercube 106 was not tilted along the Z axis.
[0057] FIGS. 7B-7C are graphs of the effect of tilt around the Z
axis in terms of tilt in arc minutes vs. error in microns. FIG. 7B
shows the effect of tilt around the Z axis versus error and image
location along the Y axis. FIG. 7C shows the effect of tilt around
the Z axis versus error and image location along the X axis.
[0058] FIGS. 8A-8C illustrate the effect of tilt about the X and Y
axis of the exemplary vision system. FIG. 8A is an additional side
view of exemplary image ray traces 210, 212, 214, 216. In FIG. 8A,
arrow 804 and dot 802 are used to depict the X and Y axes,
respectively.
[0059] FIGS. 8B-8C are graphs of the effect of tilt around the X
and Y axes in terms of tilt in arc minutes vs. error in microns.
FIG. 8B shows the effect of tilt around the X axis versus error and
image location along the Y axis. FIG. 8C shows the effect of tilt
around the Y axis versus error and image location along the X
axis.
[0060] FIG. 9 is a detailed side view of image ray traces according
to a third exemplary embodiment of the present invention. In FIG.
9, the reference position of bonding tool 104 is shown as a
reflected ray which travels from first position 914 (on image plane
112) along first optical axis 114 (shown in FIG. 1), as direct
image ray bundle 922 from first position 914 through lens element
902. Note that in this exemplary embodiment, lens element 902 has a
relatively planar, upper surface 904 and a convex lower surface
906. Direct image ray bundle 922 continues along first optical axis
114 where it then passes through upper surface 904 of lens element
902, and in turn through convex surface 906. Direct image ray
bundle 922 is then reflected onto total reflective surface 908. In
a preferred embodiment, total reflective surface 908 is a mirror.
Next, direct image ray bundle 922 travels back through lens element
902 as reflected image ray bundle 920 along second optical axis 116
(shown in FIG. 1) and onto image plane 112. It is reflected image
ray bundle 920 that is detected by imaging unit 102 (shown in FIG.
1) as image 912. Similarly, positional displacement of bonding tool
104 is also shown in FIG. 9 and is illustrated by the path of
direct image ray bundles 918, 924 from second position 910 to
second viewed position 916.
[0061] Referring to FIG. 10A, a perspective view of yet another
exemplary embodiment of the present invention is illustrated. In
FIG. 10A, multiple cornercube offset tools 1014, 1020, 1026 and
respective lens sets 1016/1018, 1022/1024, 1028/1030, are used as
an alignment means to improve the accuracy of die attach and
pick/place of assemblies, such as die 1008, 1010, 1012. This will,
in effect, replace a conventional up-looking camera (i.e., a die
camera--not shown) found in most conventional mid to high accuracy
placement (die attach and pick/place) equipment. In the exemplary
embodiment, ganged multiple cornercubes 1014, 1020, 1026 with
varied lens separation distances, 1017, 1023, 1029, respectively,
provide an indirect image of a location of die 1008, 1010, 1012,
respectively. It is understood by those of skill in the art that
only one die is viewed at a time. The use of multiple cornercube
offset tool/lens combinations allows for use with a variety of
different sized die. In other respects, such as the materials used,
the method of reflection, etc., this exemplary embodiment is
similar to the first exemplary embodiment.
[0062] As mentioned above, this variation of the first exemplary
embodiment accommodates various die sizes which these types of
equipment are required to accept and place. In this exemplary
embodiment, down looking optical detector 1002, such as a camera,
(i.e., a substrate camera) views features on the downward side of
the component to be placed, such as die, 1008, 1101, or 1012. These
features of die 1008, 1010, 1012, can then be identified via a
vision system (not shown) to accurately place the die on the
substrate (not shown) using pick tool 1004 based in part on the
predetermined distance 1006 between pick/place tool 1004 and
optical detector 1002. It is understood by those of skill in the
art, that pick tool 1004 may be either a rotating or non-rotating
pick tool. This exemplary embodiment further preserves the optical
advantages with respect to accuracy of the cornercube alignment
described above in the first exemplary embodiment.
[0063] FIG. 10B is a plan view of the exemplary embodiment
illustrated in FIG. 10A. In FIG. 10B, cornercube offset tools 1014,
1020, 1026 are placed adjacent one another to form assembly 1015.
Cornercube offset tools 1014, 1020, 1026 may be bonded to one
another, if desired using conventional adhesive means, or may be
held in alignment with one another using a mechanical device, such
as a clamp or a containment assembly, for example. The latter
approach allowing for simple replacement of individual
cornercube/lens assemblies to accommodate different sized die, as
desired. Although the exemplary embodiment is shown with three
cornercube offset tools, it is understood that at least two
cornercube offset tools may be used.
[0064] Lenses 1016, 1018, 1022, 1024, 1028, 1030 may be formed from
a unitary optical member rather than individual lenses if desired
to simplify assembly of the system. Such an approach is shown in
FIGS. 10C-10D. As shown in FIG. 10C, lens sheet 1040 has imbedded
within optical members 1016a, 1018a, 1022a, 1024a, 1028a, 1030a
equivalent to individual lenses 1016, 1018, 1022, 1024, 1028,
1030.
[0065] Although the invention has been described with reference to
exemplary embodiments, it is not limited thereto. Rather, the
appended claims should be construed to include other variants and
embodiments of the invention, which may be made by those skilled in
the art without departing from the true spirit and scope of the
present invention.
* * * * *